Two of the Kentucky mines inspected are owned by Alpha Natural Resources, and both were previously owned by Massey Energy, before Alpha bought the company in June.

MSHA began the special impact inspections in response to the explosion at the Massey-owned Upper Big Branch Mine in West Virginia, which killed twenty-nine miners. Since then, the agency says it’s conducted more than 300 impact inspections, which have resulted in more than 5,500 citations.